I think ideally you would want to structure this somewhat like a seed funding round where you and the other people who will be working on this retain somewhere

I think ideally you would want to structure this somewhat like a seed funding round where you and the other people who will be working on this retain somewhere between 50-70% of the equity after spinning off and injecting new funding. However, based on the situation and investor profile you will probably have a hard time getting to think of you as anything more than an employee. Be prepared to walk.